Must now the size of your block and the size of each square. Jelly Rolls are 2.5"
Count the number of squares in each block then multipy that by the number of blocks Measure the length of each strip in the Jelly roll and divide by the size of the square to see how many squares you will get in a strip.
Lets say you have 30 blocks and each block requires 12 squares 30 x 12 = 360
Each square is 2.5" (the width of the jelly roll) Strips are 42" 42" divided by 2.5 is 16.8
So 16 squares from each jelly roll strip. Divide the 16 into 360 and you get 22+ strips.